The present invention relates to a force characterization device, and more particularly to a test flexure for use with a coordinate measuring machine (CMM) or other contact measuring instrument to gauge the force applied by the measuring probe.
CMMs are extremely useful devices for identifying and certifying the shape and dimensions of a variety of mechanical components. These devices typically include a mechanical contact probe that is positioned through a support structure and applies a contact force to the component under test. The CMM may operate in a touch-trigger mode (also known as a switching mode), in which the probe is simply positioned to contact the component under test at a number of discrete coordinates, or in a scanning mode (also known as a continuous measuring mode), in which the probe moves in continuous contact across the component under test while measuring the position of the probe. In either mode of operation, the function of the CMM is to determine the shape and dimensions of the component under test based on the position of the contact probe. The contact nature of the system results in forces of varying magnitude and direction being applied to the component. In the scanning mode, the probe may move at velocities as high as 100 millimeters per second, which tends to cause rather significant variations in the contact force applied by the probe to the component under test. Since these force variations tend to degrade the quality of the measurement results in the absence of a compensation scheme of some kind, the CMM must be operated at slower speeds for measurements to be reliable and accurate, which increases the time required to perform a measurement cycle.
Accordingly, there is a need in the art for a force characterization device that is operable with a CMM to measure contact forces, and particularly to determine the dynamic force variations of the contact probe in the continuous scanning mode of operation.
The present invention is a force characterization device utilizing a flexure-based element, herein after referred to as a xe2x80x9cflexure,xe2x80x9d having a compliant portion and a solid portion. During operation of a coordinate measuring machine (CMM) on the solid portion of the flexure, a first capacitance probe detects displacement of the solid portion of the flexure in a first dimension and a second capacitance probe detects displacement of the solid portion of the flexure in a second dimension perpendicular to the first dimension. The detected displacements in the first and second dimensions of the solid portion of the flexure are correlated to forces applied to the flexure in the first and second dimensions based on the detected displacements and the predetermined spring constant of the compliant portion of the flexure. A total applied force is determined based on the forces applied to the flexure in the first and second dimensions. The flexure may be utilized for touch-trigger operations or scanning operations of the CMM. For scanning operations, a normal force applied and a coefficient of friction between the contact probe of the CMM and the solid portion of the flexure may be determined from the total applied force and the forces applied in the first and second dimensions.